Monocular camera systems are limited in their ability to represent three dimensional data in the camera's two-dimensional focal plane array. The camera's image of the world appears flat without any depth-of-field. The algorithmic techniques for recovering the lost depth-of-field are application dependent and work only within extremely narrow bounds—they are not globally robust. For example, structure from motion and temporal stereo matching can be used to reconstruct a depth image from a monocular camera with differential position. The camera must be moving with an inter-frame coherence and the movements must be tracked in real-world coordinates, usually with an inertial measurement unit. Other examples, such as dichromatic reflectance, Gouraud shading, and flat earth models require controlled scene illumination and a stationary camera position.